EKG Basics

Dr. Joshi

Objectives History Review of conduction system How EKG is done Normal EKGs Abnormal EKGs

History Einthoven assigned the letters P, Q, R, S

and T to the various deflections, and described the electrocardiographic features of a number of cardiovascular disorders.

In 1924, he was awarded the Nobel Prize in Medicine for his discover

What is an EKG?The electrocardiogram (EKG) is a representation of the electrical events of the cardiac cycle.

Each event has a distinctive waveform, the study of which can lead to greater insight into a patient’s cardiac pathophysiology.

The Normal Conduction System

What types of pathology can we identify and study from EKGs?

Arrhythmias Heart Blocks Myocardial ischemia and infarction Pericarditis Chamber hypertrophy Electrolyte disturbances (i.e.

hyperkalemia, hypokalemia) Drug toxicity (i.e. digoxin and drugs which

prolong the QT interval)

EKG Leads : Eyes Looking at the Heart

Leads are electrodes which measure the difference in electrical potential between either:

1. Two different points on the body (bipolar leads)1. Two different points on the body (bipolar leads)

2. One point on the body and a virtual reference point 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of with zero electrical potential, located in the center of the heart (unipolar leads)the heart (unipolar leads)

EKG Leads

The standard EKG has 12 leads: 3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from which it looks at the heart.which it looks at the heart.

Standard Limb Leads

Standard Limb Leads

Augmented Limb Leads

Augmented Limb leads30

90

-150

All Limb Leads

Precordial Leads

Adapted from: www.numed.co.uk/electrodepl.html

Precordial Leads

Summary of Leads

Limb Leads Precordial Leads

Bipolar I, II, III(standard limb leads)

-

Unipolar aVR, aVL, aVF (augmented limb leads)

V1-V6

Anatomic Groups(Septum)

Anatomic Groups(Anterior Wall)

Anatomic Groups(Lateral Wall)

Anatomic Groups(Inferior Wall)

Anatomic Groups(Summary)

Normal EKG

How to read EKG? Rate Rhythm Axis P wave PR interval QRS complexes ST segment T waves QT intervals

Rate 300 / big Square

1500/ small square

Rule of 10 seconds

What is the heart rate?

www.uptodate.com

300/6 = 50 bpm

What is the heart rate?

(300 / ~ 4) = ~ 75 bpm

www.uptodate.com

What is the heart rate?

(300 / 1.5) = 200 bpm

10 Second RuleAs most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60

seconds.

This method works well for irregular rhythms.

What is the heart rate?

The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

33 x 6 = 198 bpm

The QRS Axis

The QRS axis represents the net overall direction of the heart’s electrical activity.

Abnormalities of axis can hint at:Ventricular enlargementConduction blocks (i.e. hemiblocks)

The QRS AxisBy near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.

-30° to -90° is referred to as a left axis deviation (LAD)

+90° to +180° is referred to as a right axis deviation (RAD)

Determining the Axis

Predominantly Positive

Predominantly Negative

Equiphasic

Quadrant Approach

What is the normal axis?A. 0 degrees to 180 degrees B. 0 degrees to +90 degrees C. -30 degrees to +90 degrees D. -90 degrees to +90 degrees E. -90 degrees to +30 degrees

Answer: c , minus 30 degrees to + 90 degrees

Quadrant Approach: Example 1

The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/

What is the Axis? Right Axis Deviation Left Axis Deviation Indeterminate Axis Normal AxisAnswer: Right Axis Deviation Why?

Lead I is predominantly negative Lead aVF is positive “ Reaching”

Quadrant Approach Example 2

What is the axis? A. -100 degrees B. -30 degrees C. +15 degrees D. +90 degrees E. Indeterminate

Answer: D, Lead 1 Isoelectric and Lead aVF is positive, and therefore 90 degrees

Quadrant Approach: Example 3

What is the diagnosis? Left Axis Right Axis Indeterminate Axis Normal Axis

Answer: Indeterminate axis, Reason being lead 1, aVL and aVF are isoelectric.

Quadrant Approach: Example 4

What is the answer? Left Axis Deviation Right Axis Deviation Indeterminate axis Normal Axis

Answer: Left axis deviation Lead I positive, and aVF negative

(leaving)

P wave and PR interval It is important to remember that the P

wave represents the sequentialactivation of the right and left atria, and it is common to see notched or biphasic P waves of right and left atrial activation.

P duration < 0.12 sec P amplitude < 2.5 mm Frontal plane P wave axis: 0o to +75o May see notched P waves in frontal plane PR = less than 20 miliseconds

QRS complexes The QRS represents the simultaneousactivation of

the right and left ventricles, although most of the QRS waveform is derived from the larger left ventricular musculature.

QRS duration < 0.10 sec QRS amplitude is quite variable from lead to lead

and from person to person. Two determinates of QRS voltages are:

Size of the ventricular chambers (i.e., the larger the chamber, the larger the voltage)

Proximity of chest electrodes to ventricular chamber (the closer,the larger the voltage)

EKG in MI is important but …… Poor sensitivity for Myocardial Infarction

 (40-50%)

3-10% of MI patients have initial normal EKG

25% of patients with missed MI had misread EKG

EKG Findings you dare not miss !

Acute inferior STEMI

A 55 year old man with 4 hours of "crushing" chest pain

A 63 year old woman with 10 hours of chest pain and sweating

Acute anterior STEMI

A 60 year old man with 5 hours of chest pain and diaphoresis

Anterolateral STEMI

A 60 year old woman with 3 hours of chest pain

Acute posterior MI

A 79 year old man with 5 hours of chest pain

New LBBB, Inferior MI

A 70 year old man with exercise intolerance

Complete heart block

An 82 year old lady with dizzy spells !

AF with complete Heart block

75 y o male with blood pressure 60/40

Ventricular tachycardia

87 yo man with hx of recurrent syncope

Sinus Arrest

64 yo male who missed a session of HD

69 yo male with syncope.

Wenkebach

What is this?

Early Repolarization

Right Bundle Branch Block (RBBB)

"Complete" RBBB has a QRS duration >0.12s Close examination of QRS complex in various

leads reveals that the terminal forces (i.e., 2nd half of QRS) are oriented rightward and anteriorly because the right ventricle is depolarized after the left ventricle. This means the following: Terminal R' wave in lead V1 (usually see rSR' complex)

indicating late anterior forces Terminal S waves in leads I, aVL, V6 indicating late

rightward forces Terminal R wave in lead aVR indicating late rightward

forces The frontal plane QRS axis in RBBB should be in

the normal range (i.e., -30 to +90 degrees

RBBB

Left Bundle Branch Block(LBBB)

Complete" LBBB" has a QRS duration >0.12s. Close examination of QRS complex in various

leads reveals that the terminal forces (i.e., 2nd half of QRS) are oriented leftward and posteriorly because the left ventricle is depolarized after the right ventricle. Terminal S waves in lead V1 indicating late posterior

forces Terminal R waves in lead I, aVL, V6 indicating late

leftward forces; usually broad, monophasic R waves

LBBB

LAFB LAFB is the most common of the

intraventricular conduction defects. It is recognized by

1) left axis deviation; 2) rS complexes in II, III, aVF; and 3) small q in I and/or aVL.

LAFB

Left Posterior Fascicular Block Rare Right axis deviation in the frontal plane

(usually > +100 degrees) rS complex in lead I qR complexes in leads II, III, aVF, with R in

lead III > R in lead II QRS duration usually <0.12s unless

coexisting RBBB

Left Posterior Fascicular Block(LPFB)

Bifascicular Blocks

RBBB plus either LAFB (common) orLPFB (uncommon)

Features of RBBB plus frontal plane features of the fascicular block (axisdeviation, etc.)

Bifascicular Block

Right Atrial Enlargement RAE is recognized by the tall (>2.5mm) P

waves in leads II, III, aVF. RVH is likely because of right axis

deviation (+100 degrees) and the Qr (or rSR') complexes in V1-2.

Right Atrial Enlargement

LVH with "Strain"

Criteria for LVH Sokolow + Lyon (Am Heart J, 1949;37:161)

S V1+ R V5 or V6 > 35 mm

Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women

Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm, S V1 or V2 + R V5 or V6 > 35 mm, R I + S III > 25 mm

REMEMBER: S in V1 plus R in V5 or 6 > 35

RVH

Knowledge is beautiful

References Up to date ECG Library Alan E. Lindsay ECG learning Center Wikipedia